Earth & Sky

World rainfall harder, more frequent than thought

Around the world, rain falls harder and more frequently on average than previously thought. That’s according to climate scientist Graeme Stephens, principal investigator of the CloudSat Earth-observing satellite.

Graeme Stephens:What we’re finding is from our observations that 12 percent of the clouds on any place on Earth are producing rain that falls to the ground.

Previously, scientists thought that only 8 percent of clouds – at least those over the ocean – produced rain.

Graeme Stephens: So why do we care about that? That’s the rain from the clouds that supplies the fresh water that sustains life.

Stephens told Earth & Sky these new results suggest that it rains harder and more frequently than was previously thought, especially in winter. He added that how water rises in the sky and falls back to the surface governs the pace of global climate change.

Graeme Stephens:The most important aspects of climate change, in my mind, is how the hydrological cycle changes, where water goes, where it doesn’t go. It’s not whether the temperature warms one degree, or two degrees, or three degrees. It’s whether the water distribution changes, whether the Southwest is going to be in a more perpetual situation of drought, for example. They’re the critical issues.

Stephens and his colleagues also found that pollution makes clouds thicker and brighter. These dirty clouds reflect more sunlight and help cool the Earth. But they’re also less likely to make rain.

Stephens added that CloudSat’s instruments are so sensitive they can see inside of clouds, and they can see the difference between small cloud particles, larger raindrops, and snowflakes.

Our thanks today to NASA: explore, discover, understand.